58 Transactions of the South African Philosophical Society. 



different particles of this debris upon one another as they sink 

 deeper and deeper must produce thousands of tons of fine material 

 pre-eminently adapted for the formation of mud. Furthermore a 

 heavy shower of rain will deposit thousands of tons of water in 

 the great receiving funnel of the open mine. We have then what at 

 first sight might appear to be all that is necessary to make the mud : 

 plenty of debris, and a vast receiving surface for the water. 



A very little consideration, however, will be sufficient to convince 

 one that nothing short of a deluge could possibly convert the avail- 

 able materials into a viscous state. No sluits are allowed to 

 discharge into the open mine, so that the precipitation is pretty 

 equally distributed over the whole surface. What certainly happens 

 then, is this : the rain percolates into the debris as it descends, and is 

 absorbed by the top layers until they are saturated; and no layer 

 below can take up any of the rain directly until the layers above can 

 hold no more. In all probability six feet of debris could absorb quite 

 that number of inches of rain. Afterwards the lower layers will 

 absorb the moisture from the upper layers, by a simple drying-out 

 process ; but of course this process is the inverse of that required to 

 produce mud. The rain having ceased, evaporation begins, the 

 upper layers are dried up, and, in their turn, dry out the lower 

 layers. It seems, then, that while there is nothing in the rainfall 

 record to support the rainfall theory, neither is there any antecedent 

 probability that rain could penetrate anything like a thousand feet of 

 debris save in inappreciable quantities. This deduction may be 

 further enforced by a little arithmetic. I have said that mud rushes 

 filling up more than a thousand linear feet of tunnel are not 

 unknown.* Combining this length with the average sectional area 

 of the tunnels, say nearly 100 square feet, and remembering too 

 that sundry large chutes and offsets are also filled up at the same 

 time, we have, for a large rush, a cubic content of quite one hundred 

 thousand feet, without taking account of what mud may be still left 

 in the place from whence it came. Assuming that one-half is water, 

 it follows that at least fifty thousand cubic feet of water have to be 

 accounted for. Now the contour of the open mine is roughly twelve 

 hundred feet in length by eleven hundred in breadth, or say a 

 superficial area of about a million square feet. An inch of rain 

 falling into the open mine would only represent eighty thousand 

 cubic feet of water, whereas it is quite plain that at least this 

 quantity would have to collect into one pocket, where every particle 

 of it could act upon every other particle, before 50,000 cubic feet of 



* A mud rush some years ago in the Kimberley Mine is said to have filled 

 3,000 linear feet of tunnel. 



